潜流湿地处理不同浓度有机污水的差异分析

通过供氧平衡及物质平衡理论分析和实证研究,探讨根系泌氧、水中自带溶解氧、植物吸收营养物在湿地净化中的贡献,并通过落空运行来启动大气复氧.结果表明,当处理Ⅳ类以下地表水时,根系泌氧和水中携氧可使基质内为好氧环境、出水DO>0;植物吸收和介质吸附可使N、P去除稳定.当处理生活污水时,植物供氧不足,基质内为缺氧/厌氧环境、铵氧化细菌和亚硝酸氧化菌数量只有氨化细菌的1/1 000～1/100,出水DO≈0,使基质易堵塞;植物吸收和介质吸附有限,氮去除率≤20%;磷去除率随介质吸附容量的饱和逐渐下降,运行前3个月去除率为54%,运行1a以后降低到5%.潜流湿地处理生活污水时污染负荷远大于植物供氧和吸收营养物的上限,是其存在技术局限的根本原因.启动大气复氧是湿地工艺改进的一个重要方向,预沉-常规湿地对COD、NH₄⁺-N、TN、TP的去除率为79%、34%、36%、34%,预沉-落空湿地则为79%、88%、14%、69%,必须合理利用大气复氧才能实现去除总氮的最终目的.

Difference Between Subsurface Wetlands for Different Water Treatment

By analysis of oxygen balance and material balance as well as empirical study, contribution of root oxygenation, water-carried oxygen and plant absorbance of nutrient in subsurface wetlands (SW) was examined, and free drainage in substrate was also adopted to check its effect on air transfer. The results showed that plant play important role when SW treating surface water with low concentration of contaminants. In such case, root oxygenation and water-carried oxygen sustains the substrate aerobic and so effluent DO > 0; N and P removal is stable for plant absorbance and media adsorption. However, in the case of higher load, namely domestic wastewater, role of root oxygenation becomes < or = 20% and effluent DO approximately 0. It is also found that amount of nitrate and nitrite bacteria are only 1/1 000 - 1/100 of amonifying bacteria in saturated substrate, which has strong negative effect on anti-clogging and nitrogen removal. Nitrogen removal percentage is often < or = 20%. Phosphorous initial removal percentage is 54%, but decreases to 5% after a year operation for the consumption of absorption capacity. Because pollutants load is too high for root oxygenation and plant absorbance and media absorption, limitations do exist in SW for domestic wastewater treatment. It is necessary to take use of air-reoxygenation in SW. The results showed that COD, NH4(+) -N, TN and TP removal percentage of SW with high water lever was 79%, 34%, 36% and 34% and those of SW with free drainage was 79%, 88%, 14%, 69%, which suggest that only air transfer is used properly, total nitrogen removal could be achieved in single-stage wetland.